(1) Field of the Invention
The present invention relates to a method and an apparatus for driving a capacitive-type load. More particularly, it relates to a method and an apparatus for driving, for example, a piezoelectric actuator, electrostrictive actuator and the like used in a fuel injection valve of an internal combustion engine.
(2) Description of the Related Art
In a known driving circuit for a piezoelectric actuator including piezoelectric elements, the circuit comprises a thyristor and a coil connected in series, one of which is connected to the actuator in series and the other is connected to the actuator in parallel. This circuit utilizes a resonance phenomenon of the coil, and therefore, when a negative voltage is applied to the piezoelectric actuator, the actuator is deteriorated by polarization. Thus a problem of assuring the initial characteristic arises. Further, in the above-mentioned circuit, the voltage of the high voltage power source must be changed to control the expansion or contraction of the piezoelectric actuator. Also, the response characteristic thereof is not satisfactory. To eliminate these problems, another circuit which comprises an added amplifier and a transistor circuit is known. However, this circuit has a complicated structure and a high production cost, has a high energy-consumption when driving, caused by a resistance, and thus has a poor power efficiency plus heat generation occurs. The technical background for the present invention is disclosed in Japanese Patent Application No. 60-81432 (TAKIGAWA et al. U.S. application Ser. No. 850,696 filed on Apr. 11, 1986).